The present invention relates to fluid flow systems, and in particular nuclear reactor coolant systems.
In many nuclear power plants, power is generated in a plurality of individual loops, and differences will typically exist between loops as regards temperatures and steam generation rates. Such differences may be caused by differences in reactor coolant flows, steam generator heat transfer rates and steam piping differential pressures.
As a result of such differences, the coolant temperature at the inlets to the reactor core is not uniform, and this will cause at least small differences in power distribution and fuel burnup across the core. The relative differences in power distribution increase as system power demand decreases, and can reach levels at which power distribution alarms are initiated, indicating that some corrective measures must be taken.
Many reactor installations having a plurality of coolant loops are equipped with a steam generating system composed of a plurality of steam generators, one for each coolant loop, and a feedwater heating system composed of pumps and heat exchangers to supply heated feedwater to the steam generators. It is known that the overall heat transfer behavior of the steam generating system can be adjusted by varying the temperature of the feedwater supplied to the steam generators. This control capability has been considered for improving power availability when reactor core burnup is being extended beyond the normal fuel cycle burnup. However, in existing systems, all steam generators receive feedwater at the same temperature.